This invention relates to helical gears used for an infinitely variable transmission for vehicles.
An infinitely variable transmission (IVT) for vehicles which combines a fixed speed ratio transmission and a planetary gear set with a continuously variable transmission (CVT) in order to expand the speed change region of the continuously variable transmission (CVT) is disclosed in U.S. Pat. No. 5,935,039 as well as in Tokkai Hei 9-210175 published in 1997, Tokkai Hei 10-220551 published in 1998, and Tokkai Hei 11-63139 published in 1999 respectively by the Japanese Patent Office.
In these IVT, helical gears are used for the gears of the planetary gear set, the output gears of the fixed speed ratio transmission and CVT, respectively to suppress noise and vibration. The helical gears generate a thrust force according to the turning direction of the tooth trace, and the transfer direction of the torque.
Therefore, depending on the direction of the turning direction of the tooth trace of the helical gears, the thrust force generated by the gears due to torque transmission may be concentrated in one direction. Such a concentration of the thrust force lowers the durability of the bearings supporting the thrust force, increases the friction of the gears, and adversely affects the power transmission efficiency of the IVT.
Moreover, if the bearings are made larger in order to bear the thrust force, the size of IVT will increase.
It is therefore an object of this invention to prevent concentration of the thrust force in the IVT.
In order to achieve the above object, this invention provides an infinitely variable transmission interposed between an engine and a drive shaft of a vehicle to transmit an engine torque to the drive shaft, comprising a first shaft joined to the engine, a second shaft disposed parallel to the first shaft, a fixed speed ratio transmission comprising a first rotation element supported on the second shaft which outputs the rotation of the first shaft at a fixed speed ratio, a continuously variable transmission comprising a second rotation element supported on the second shaft which outputs the rotation of the first shaft at an arbitrary speed ratio, a planetary gear set disposed between the first rotation element and the second rotation element, a final output gear, and a transmitting gear.
The first rotation element and second rotation element are supported free to rotate relative to each other.
The planetary gear set comprises a sun gear joined to the second rotation element, a planet carrier joined to the first rotation element and a ring gear which varies a rotation direction and a rotation speed according to a rotation speed difference between the sun gear and the planet carrier.
The planet carrier supports a planet gear which is meshed with the sun gear and the ring gear, and revolves around the sun gear together with the planet carrier.
The sun gear, ring gear, planet gear, final output gear and transmitting gear are helical gears.
The final output gear is joined to the ring gear and disposed between the planetary gear set and second rotation element.
The transmitting gear meshes with the final output gear and transmits a rotation of the final output gear to the drive shaft.
The ring gear and the final output gear have tooth traces with which, when a torque is transmitted from the engine to the drive shaft, a thrust force exerted by the planet gear on the ring gear and a thrust force exerted by the transmitting gear on the final output gear act in opposite directions.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.